'JetBrains, You're scaring me. The Rust plugin deprecation situation'

I'm still confused why they keep making the language specific apps, or why people use them (instead of Idea Ultimate) for that matter.

It makes sense to deprecate something they will no longer maintain as it will probably rot and give users a bad experience, major plugins like rust needs continual nurturing and that is costly. Is the old one open source? can't someone pick it up and run with it?